# Helpers for argument validation

## The `match_arg()` function

    match_arg(
      arg = "lo",
      choices = c("loooong", "else"),
      several.ok = FALSE,
      none.ok = FALSE
    )
    #> [1] "loooong"

## The `check_covariance_matrix()` function

    check_covariance_matrix(
      matrix(c(1, 2, 2, 1), nrow = 2) * -1
    )
    #> [1] "Must have positive eigenvalues only"

## The `check_correlation_matrix()` function

    check_correlation_matrix(
      matrix(c(1, 0, 0, 0), nrow = 2)
    )
    #> [1] "Must have ones on the diagonal"

## The `check_transition_probability_matrix()` function

    check_correlation_matrix(
      matrix(c(1, 1, 0, 1), nrow = 2)
    )
    #> [1] "Must be symmetric"

## The `check_probability_vector()` function

    check_probability_vector(
      1:5 / sum(1:5),
      len = 4
    )
    #> [1] "Must have length 4, but has length 5"